A sysadmin twitch about dump

February 4, 2007

In dump (and ufsdump, and other close cousins) you can specify the filesystem that you want to dump in two ways: by the name of its mountpoint, or by the name of the (raw) device that it's on. One of my little twitches is that I always specify the filesystem to dump by its mountpoint. Like a lot of my little twitches, this has a history behind it.

The problem is that at least some old versions of dump were perfectly willing to write their output to anything, including raw disk devices, and they had defaults for what filesystem to dump (and where to dump it to), and as a bonus they had an argument parsing scheme that made accidents really easy.

So, if you accidentally wrote, say:

dump 0usf /dev/rmt0 /dev/rrf0g

You could destroy a filesystem, as some people did once.

However, dump can't write to directories. So once I read that sad story in comp.risks, I started always using the filesystem mount point instead of the raw device; that way if I made a mistake, dump would just die with complaints that it couldn't write to its output.

(Another lesson that one can draw from this is to always run dumps from an account that only has read access to the raw disk devices.)

Written on 04 February 2007.
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Last modified: Sun Feb 4 23:10:18 2007
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